Mailing List Archive

[PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

This patch introduces a helper the main purpose of which is to check
if a domain is using IOREQ server(s).

On Arm the current benefit is to avoid calling handle_io_completion()
(which implies iterating over all possible IOREQ servers anyway)
on every return in leave_hypervisor_to_guest() if there is no active
servers for the particular domain.
Also this helper will be used by one of the subsequent patches on Arm.

This involves adding an extra per-domain variable to store the count
of servers in use.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
CC: Julien Grall <julien.grall@arm.com>

---
Please note, this is a split/cleanup/hardening of Julien's PoC:
"Add support for Guest IO forwarding to a device emulator"

Changes RFC -> V1:
- new patch

Changes V1 -> V2:
- update patch description
- guard helper with CONFIG_IOREQ_SERVER
- remove "hvm" prefix
- modify helper to just return d->arch.hvm.ioreq_server.nr_servers
- put suitable ASSERT()s
- use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
- remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
---
xen/arch/arm/traps.c | 15 +++++++++------
xen/common/ioreq.c | 7 ++++++-
xen/include/xen/ioreq.h | 14 ++++++++++++++
xen/include/xen/sched.h | 1 +
4 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 507c095..a8f5fdf 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
struct vcpu *v = current;

#ifdef CONFIG_IOREQ_SERVER
- bool handled;
+ if ( domain_has_ioreq_server(v->domain) )
+ {
+ bool handled;

- local_irq_enable();
- handled = handle_io_completion(v);
- local_irq_disable();
+ local_irq_enable();
+ handled = handle_io_completion(v);
+ local_irq_disable();

- if ( !handled )
- return true;
+ if ( !handled )
+ return true;
+ }
#endif

if ( likely(!v->arch.need_flush_to_ram) )
diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
index bcd4961..a72bc0e 100644
--- a/xen/common/ioreq.c
+++ b/xen/common/ioreq.c
@@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
struct ioreq_server *s)
{
ASSERT(id < MAX_NR_IOREQ_SERVERS);
- ASSERT(!s || !d->ioreq_server.server[id]);
+ ASSERT(d->ioreq_server.server[id] ? !s : !!s);

d->ioreq_server.server[id] = s;
+
+ if ( s )
+ d->ioreq_server.nr_servers++;
+ else
+ d->ioreq_server.nr_servers--;
}

#define GET_IOREQ_SERVER(d, id) \
diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
index 7b03ab5..0679fef 100644
--- a/xen/include/xen/ioreq.h
+++ b/xen/include/xen/ioreq.h
@@ -55,6 +55,20 @@ struct ioreq_server {
uint8_t bufioreq_handling;
};

+#ifdef CONFIG_IOREQ_SERVER
+static inline bool domain_has_ioreq_server(const struct domain *d)
+{
+ ASSERT((current->domain == d) || atomic_read(&d->pause_count));
+
+ return d->ioreq_server.nr_servers;
+}
+#else
+static inline bool domain_has_ioreq_server(const struct domain *d)
+{
+ return false;
+}
+#endif
+
struct ioreq_server *get_ioreq_server(const struct domain *d,
unsigned int id);

diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index f9ce14c..290cddb 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -553,6 +553,7 @@ struct domain
struct {
spinlock_t lock;
struct ioreq_server *server[MAX_NR_IOREQ_SERVERS];
+ unsigned int nr_servers;
} ioreq_server;
#endif
};
--
2.7.4
RE: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
> -----Original Message-----
> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
> Sent: 15 October 2020 17:44
> To: xen-devel@lists.xenproject.org
> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini <sstabellini@kernel.org>;
> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
>
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>
> This patch introduces a helper the main purpose of which is to check
> if a domain is using IOREQ server(s).
>
> On Arm the current benefit is to avoid calling handle_io_completion()
> (which implies iterating over all possible IOREQ servers anyway)
> on every return in leave_hypervisor_to_guest() if there is no active
> servers for the particular domain.
> Also this helper will be used by one of the subsequent patches on Arm.
>
> This involves adding an extra per-domain variable to store the count
> of servers in use.
>
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> CC: Julien Grall <julien.grall@arm.com>
>
> ---
> Please note, this is a split/cleanup/hardening of Julien's PoC:
> "Add support for Guest IO forwarding to a device emulator"
>
> Changes RFC -> V1:
> - new patch
>
> Changes V1 -> V2:
> - update patch description
> - guard helper with CONFIG_IOREQ_SERVER
> - remove "hvm" prefix
> - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
> - put suitable ASSERT()s
> - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
> - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
> ---
> xen/arch/arm/traps.c | 15 +++++++++------
> xen/common/ioreq.c | 7 ++++++-
> xen/include/xen/ioreq.h | 14 ++++++++++++++
> xen/include/xen/sched.h | 1 +
> 4 files changed, 30 insertions(+), 7 deletions(-)
>
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 507c095..a8f5fdf 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
> struct vcpu *v = current;
>
> #ifdef CONFIG_IOREQ_SERVER
> - bool handled;
> + if ( domain_has_ioreq_server(v->domain) )
> + {
> + bool handled;
>
> - local_irq_enable();
> - handled = handle_io_completion(v);
> - local_irq_disable();
> + local_irq_enable();
> + handled = handle_io_completion(v);
> + local_irq_disable();
>
> - if ( !handled )
> - return true;
> + if ( !handled )
> + return true;
> + }
> #endif
>
> if ( likely(!v->arch.need_flush_to_ram) )
> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
> index bcd4961..a72bc0e 100644
> --- a/xen/common/ioreq.c
> +++ b/xen/common/ioreq.c
> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
> struct ioreq_server *s)
> {
> ASSERT(id < MAX_NR_IOREQ_SERVERS);
> - ASSERT(!s || !d->ioreq_server.server[id]);
> + ASSERT(d->ioreq_server.server[id] ? !s : !!s);

That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?

Paul

>
> d->ioreq_server.server[id] = s;
> +
> + if ( s )
> + d->ioreq_server.nr_servers++;
> + else
> + d->ioreq_server.nr_servers--;
> }
>
> #define GET_IOREQ_SERVER(d, id) \
> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
> index 7b03ab5..0679fef 100644
> --- a/xen/include/xen/ioreq.h
> +++ b/xen/include/xen/ioreq.h
> @@ -55,6 +55,20 @@ struct ioreq_server {
> uint8_t bufioreq_handling;
> };
>
> +#ifdef CONFIG_IOREQ_SERVER
> +static inline bool domain_has_ioreq_server(const struct domain *d)
> +{
> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
> +

This seems like an odd place to put such an assertion.

> + return d->ioreq_server.nr_servers;
> +}
> +#else
> +static inline bool domain_has_ioreq_server(const struct domain *d)
> +{
> + return false;
> +}
> +#endif
> +

Can this be any more compact? E.g.

return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;

?

> struct ioreq_server *get_ioreq_server(const struct domain *d,
> unsigned int id);
>
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index f9ce14c..290cddb 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -553,6 +553,7 @@ struct domain
> struct {
> spinlock_t lock;
> struct ioreq_server *server[MAX_NR_IOREQ_SERVERS];
> + unsigned int nr_servers;
> } ioreq_server;
> #endif
> };
> --
> 2.7.4
Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
On 20.10.20 13:51, Paul Durrant wrote:

Hi Paul.

Sorry for the late response.

>
>> -----Original Message-----
>> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
>> Sent: 15 October 2020 17:44
>> To: xen-devel@lists.xenproject.org
>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini <sstabellini@kernel.org>;
>> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
>> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
>> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
>> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
>>
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> This patch introduces a helper the main purpose of which is to check
>> if a domain is using IOREQ server(s).
>>
>> On Arm the current benefit is to avoid calling handle_io_completion()
>> (which implies iterating over all possible IOREQ servers anyway)
>> on every return in leave_hypervisor_to_guest() if there is no active
>> servers for the particular domain.
>> Also this helper will be used by one of the subsequent patches on Arm.
>>
>> This involves adding an extra per-domain variable to store the count
>> of servers in use.
>>
>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>> CC: Julien Grall <julien.grall@arm.com>
>>
>> ---
>> Please note, this is a split/cleanup/hardening of Julien's PoC:
>> "Add support for Guest IO forwarding to a device emulator"
>>
>> Changes RFC -> V1:
>> - new patch
>>
>> Changes V1 -> V2:
>> - update patch description
>> - guard helper with CONFIG_IOREQ_SERVER
>> - remove "hvm" prefix
>> - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
>> - put suitable ASSERT()s
>> - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
>> - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
>> ---
>> xen/arch/arm/traps.c | 15 +++++++++------
>> xen/common/ioreq.c | 7 ++++++-
>> xen/include/xen/ioreq.h | 14 ++++++++++++++
>> xen/include/xen/sched.h | 1 +
>> 4 files changed, 30 insertions(+), 7 deletions(-)
>>
>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>> index 507c095..a8f5fdf 100644
>> --- a/xen/arch/arm/traps.c
>> +++ b/xen/arch/arm/traps.c
>> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
>> struct vcpu *v = current;
>>
>> #ifdef CONFIG_IOREQ_SERVER
>> - bool handled;
>> + if ( domain_has_ioreq_server(v->domain) )
>> + {
>> + bool handled;
>>
>> - local_irq_enable();
>> - handled = handle_io_completion(v);
>> - local_irq_disable();
>> + local_irq_enable();
>> + handled = handle_io_completion(v);
>> + local_irq_disable();
>>
>> - if ( !handled )
>> - return true;
>> + if ( !handled )
>> + return true;
>> + }
>> #endif
>>
>> if ( likely(!v->arch.need_flush_to_ram) )
>> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
>> index bcd4961..a72bc0e 100644
>> --- a/xen/common/ioreq.c
>> +++ b/xen/common/ioreq.c
>> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
>> struct ioreq_server *s)
>> {
>> ASSERT(id < MAX_NR_IOREQ_SERVERS);
>> - ASSERT(!s || !d->ioreq_server.server[id]);
>> + ASSERT(d->ioreq_server.server[id] ? !s : !!s);
> That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?

ok, looks like it will work.


> Paul
>
>> d->ioreq_server.server[id] = s;
>> +
>> + if ( s )
>> + d->ioreq_server.nr_servers++;
>> + else
>> + d->ioreq_server.nr_servers--;
>> }
>>
>> #define GET_IOREQ_SERVER(d, id) \
>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
>> index 7b03ab5..0679fef 100644
>> --- a/xen/include/xen/ioreq.h
>> +++ b/xen/include/xen/ioreq.h
>> @@ -55,6 +55,20 @@ struct ioreq_server {
>> uint8_t bufioreq_handling;
>> };
>>
>> +#ifdef CONFIG_IOREQ_SERVER
>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>> +{
>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
>> +
> This seems like an odd place to put such an assertion.

I might miss something or interpreted incorrectly but these asserts are
the result of how I understood the review comment on previous version [1].

I will copy a comment here for the convenience:
"This is safe only when d == current->domain and it's not paused,
or when they're distinct and d is paused. Otherwise the result is
stale before the caller can inspect it. This wants documenting by
at least a comment, but perhaps better by suitable ASSERT()s."


>
>> + return d->ioreq_server.nr_servers;
>> +}
>> +#else
>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>> +{
>> + return false;
>> +}
>> +#endif
>> +
> Can this be any more compact? E.g.
>
> return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;
>
> ?
I have got a compilation error this way (if CONFIG_IOREQ_SERVER is
disabled):

...xen/4.14.0+gitAUTOINC+ee22110219-r0/git/xen/include/xen/ioreq.h:62:48:
error: ‘const struct domain’ has no member named ‘ioreq_server’
     return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;
                                                ^
as domain's ioreq_server struct is guarded by CONFIG_IOREQ_SERVER as well.


[1]
https://patchwork.kernel.org/project/xen-devel/patch/1599769330-17656-12-git-send-email-olekstysh@gmail.com/#23618623

Thank you.

--
Regards,

Oleksandr Tyshchenko
Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
On 10.11.2020 21:53, Oleksandr wrote:
>
> On 20.10.20 13:51, Paul Durrant wrote:
>
> Hi Paul.
>
> Sorry for the late response.
>
>>
>>> -----Original Message-----
>>> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
>>> Sent: 15 October 2020 17:44
>>> To: xen-devel@lists.xenproject.org
>>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini <sstabellini@kernel.org>;
>>> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
>>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
>>> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
>>> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
>>> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
>>>
>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>
>>> This patch introduces a helper the main purpose of which is to check
>>> if a domain is using IOREQ server(s).
>>>
>>> On Arm the current benefit is to avoid calling handle_io_completion()
>>> (which implies iterating over all possible IOREQ servers anyway)
>>> on every return in leave_hypervisor_to_guest() if there is no active
>>> servers for the particular domain.
>>> Also this helper will be used by one of the subsequent patches on Arm.
>>>
>>> This involves adding an extra per-domain variable to store the count
>>> of servers in use.
>>>
>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>> CC: Julien Grall <julien.grall@arm.com>
>>>
>>> ---
>>> Please note, this is a split/cleanup/hardening of Julien's PoC:
>>> "Add support for Guest IO forwarding to a device emulator"
>>>
>>> Changes RFC -> V1:
>>> - new patch
>>>
>>> Changes V1 -> V2:
>>> - update patch description
>>> - guard helper with CONFIG_IOREQ_SERVER
>>> - remove "hvm" prefix
>>> - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
>>> - put suitable ASSERT()s
>>> - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
>>> - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
>>> ---
>>> xen/arch/arm/traps.c | 15 +++++++++------
>>> xen/common/ioreq.c | 7 ++++++-
>>> xen/include/xen/ioreq.h | 14 ++++++++++++++
>>> xen/include/xen/sched.h | 1 +
>>> 4 files changed, 30 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>>> index 507c095..a8f5fdf 100644
>>> --- a/xen/arch/arm/traps.c
>>> +++ b/xen/arch/arm/traps.c
>>> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
>>> struct vcpu *v = current;
>>>
>>> #ifdef CONFIG_IOREQ_SERVER
>>> - bool handled;
>>> + if ( domain_has_ioreq_server(v->domain) )
>>> + {
>>> + bool handled;
>>>
>>> - local_irq_enable();
>>> - handled = handle_io_completion(v);
>>> - local_irq_disable();
>>> + local_irq_enable();
>>> + handled = handle_io_completion(v);
>>> + local_irq_disable();
>>>
>>> - if ( !handled )
>>> - return true;
>>> + if ( !handled )
>>> + return true;
>>> + }
>>> #endif
>>>
>>> if ( likely(!v->arch.need_flush_to_ram) )
>>> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
>>> index bcd4961..a72bc0e 100644
>>> --- a/xen/common/ioreq.c
>>> +++ b/xen/common/ioreq.c
>>> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
>>> struct ioreq_server *s)
>>> {
>>> ASSERT(id < MAX_NR_IOREQ_SERVERS);
>>> - ASSERT(!s || !d->ioreq_server.server[id]);
>>> + ASSERT(d->ioreq_server.server[id] ? !s : !!s);
>> That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?
>
> ok, looks like it will work.
>
>
>> Paul
>>
>>> d->ioreq_server.server[id] = s;
>>> +
>>> + if ( s )
>>> + d->ioreq_server.nr_servers++;
>>> + else
>>> + d->ioreq_server.nr_servers--;
>>> }
>>>
>>> #define GET_IOREQ_SERVER(d, id) \
>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
>>> index 7b03ab5..0679fef 100644
>>> --- a/xen/include/xen/ioreq.h
>>> +++ b/xen/include/xen/ioreq.h
>>> @@ -55,6 +55,20 @@ struct ioreq_server {
>>> uint8_t bufioreq_handling;
>>> };
>>>
>>> +#ifdef CONFIG_IOREQ_SERVER
>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>> +{
>>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
>>> +
>> This seems like an odd place to put such an assertion.
>
> I might miss something or interpreted incorrectly but these asserts are
> the result of how I understood the review comment on previous version [1].
>
> I will copy a comment here for the convenience:
> "This is safe only when d == current->domain and it's not paused,
> or when they're distinct and d is paused. Otherwise the result is
> stale before the caller can inspect it. This wants documenting by
> at least a comment, but perhaps better by suitable ASSERT()s."

The way his reply was worded, I think Paul was wondering about the
place where you put the assertion, not what you actually assert.

>>> + return d->ioreq_server.nr_servers;
>>> +}
>>> +#else
>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>> +{
>>> + return false;
>>> +}
>>> +#endif
>>> +
>> Can this be any more compact? E.g.
>>
>> return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;
>>
>> ?
> I have got a compilation error this way (if CONFIG_IOREQ_SERVER is
> disabled):
>
> ...xen/4.14.0+gitAUTOINC+ee22110219-r0/git/xen/include/xen/ioreq.h:62:48:
> error: ‘const struct domain’ has no member named ‘ioreq_server’
>      return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;
>                                                 ^
> as domain's ioreq_server struct is guarded by CONFIG_IOREQ_SERVER as well.

The #ifdef is unavoidable here, I agree, but it should be inside
the function's body. There's no need to duplicate the rest of it.

Jan
Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
On 11.11.20 10:08, Jan Beulich wrote:

Hi Jan

> On 10.11.2020 21:53, Oleksandr wrote:
>> On 20.10.20 13:51, Paul Durrant wrote:
>>
>> Hi Paul.
>>
>> Sorry for the late response.
>>
>>>> -----Original Message-----
>>>> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
>>>> Sent: 15 October 2020 17:44
>>>> To: xen-devel@lists.xenproject.org
>>>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini <sstabellini@kernel.org>;
>>>> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
>>>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
>>>> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
>>>> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
>>>> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
>>>>
>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>
>>>> This patch introduces a helper the main purpose of which is to check
>>>> if a domain is using IOREQ server(s).
>>>>
>>>> On Arm the current benefit is to avoid calling handle_io_completion()
>>>> (which implies iterating over all possible IOREQ servers anyway)
>>>> on every return in leave_hypervisor_to_guest() if there is no active
>>>> servers for the particular domain.
>>>> Also this helper will be used by one of the subsequent patches on Arm.
>>>>
>>>> This involves adding an extra per-domain variable to store the count
>>>> of servers in use.
>>>>
>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>> CC: Julien Grall <julien.grall@arm.com>
>>>>
>>>> ---
>>>> Please note, this is a split/cleanup/hardening of Julien's PoC:
>>>> "Add support for Guest IO forwarding to a device emulator"
>>>>
>>>> Changes RFC -> V1:
>>>> - new patch
>>>>
>>>> Changes V1 -> V2:
>>>> - update patch description
>>>> - guard helper with CONFIG_IOREQ_SERVER
>>>> - remove "hvm" prefix
>>>> - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
>>>> - put suitable ASSERT()s
>>>> - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
>>>> - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
>>>> ---
>>>> xen/arch/arm/traps.c | 15 +++++++++------
>>>> xen/common/ioreq.c | 7 ++++++-
>>>> xen/include/xen/ioreq.h | 14 ++++++++++++++
>>>> xen/include/xen/sched.h | 1 +
>>>> 4 files changed, 30 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>>>> index 507c095..a8f5fdf 100644
>>>> --- a/xen/arch/arm/traps.c
>>>> +++ b/xen/arch/arm/traps.c
>>>> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
>>>> struct vcpu *v = current;
>>>>
>>>> #ifdef CONFIG_IOREQ_SERVER
>>>> - bool handled;
>>>> + if ( domain_has_ioreq_server(v->domain) )
>>>> + {
>>>> + bool handled;
>>>>
>>>> - local_irq_enable();
>>>> - handled = handle_io_completion(v);
>>>> - local_irq_disable();
>>>> + local_irq_enable();
>>>> + handled = handle_io_completion(v);
>>>> + local_irq_disable();
>>>>
>>>> - if ( !handled )
>>>> - return true;
>>>> + if ( !handled )
>>>> + return true;
>>>> + }
>>>> #endif
>>>>
>>>> if ( likely(!v->arch.need_flush_to_ram) )
>>>> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
>>>> index bcd4961..a72bc0e 100644
>>>> --- a/xen/common/ioreq.c
>>>> +++ b/xen/common/ioreq.c
>>>> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
>>>> struct ioreq_server *s)
>>>> {
>>>> ASSERT(id < MAX_NR_IOREQ_SERVERS);
>>>> - ASSERT(!s || !d->ioreq_server.server[id]);
>>>> + ASSERT(d->ioreq_server.server[id] ? !s : !!s);
>>> That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?
>> ok, looks like it will work.
>>
>>
>>> Paul
>>>
>>>> d->ioreq_server.server[id] = s;
>>>> +
>>>> + if ( s )
>>>> + d->ioreq_server.nr_servers++;
>>>> + else
>>>> + d->ioreq_server.nr_servers--;
>>>> }
>>>>
>>>> #define GET_IOREQ_SERVER(d, id) \
>>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
>>>> index 7b03ab5..0679fef 100644
>>>> --- a/xen/include/xen/ioreq.h
>>>> +++ b/xen/include/xen/ioreq.h
>>>> @@ -55,6 +55,20 @@ struct ioreq_server {
>>>> uint8_t bufioreq_handling;
>>>> };
>>>>
>>>> +#ifdef CONFIG_IOREQ_SERVER
>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>>> +{
>>>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
>>>> +
>>> This seems like an odd place to put such an assertion.
>> I might miss something or interpreted incorrectly but these asserts are
>> the result of how I understood the review comment on previous version [1].
>>
>> I will copy a comment here for the convenience:
>> "This is safe only when d == current->domain and it's not paused,
>> or when they're distinct and d is paused. Otherwise the result is
>> stale before the caller can inspect it. This wants documenting by
>> at least a comment, but perhaps better by suitable ASSERT()s."
> The way his reply was worded, I think Paul was wondering about the
> place where you put the assertion, not what you actually assert.

Shall I put the assertion at the call sites of this helper instead?


>
>
>>>> + return d->ioreq_server.nr_servers;
>>>> +}
>>>> +#else
>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>>> +{
>>>> + return false;
>>>> +}
>>>> +#endif
>>>> +
>>> Can this be any more compact? E.g.
>>>
>>> return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;
>>>
>>> ?
>> I have got a compilation error this way (if CONFIG_IOREQ_SERVER is
>> disabled):
>>
>> ...xen/4.14.0+gitAUTOINC+ee22110219-r0/git/xen/include/xen/ioreq.h:62:48:
>> error: ‘const struct domain’ has no member named ‘ioreq_server’
>>      return IS_ENABLED(CONFIG_IOREQ_SERVER) && d->ioreq_server.nr_servers;
>>                                                 ^
>> as domain's ioreq_server struct is guarded by CONFIG_IOREQ_SERVER as well.
> The #ifdef is unavoidable here, I agree, but it should be inside
> the function's body. There's no need to duplicate the rest of it.


Got it, will do.


--
Regards,

Oleksandr Tyshchenko
Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
On 11.11.2020 09:41, Oleksandr wrote:
>
> On 11.11.20 10:08, Jan Beulich wrote:
>
> Hi Jan
>
>> On 10.11.2020 21:53, Oleksandr wrote:
>>> On 20.10.20 13:51, Paul Durrant wrote:
>>>
>>> Hi Paul.
>>>
>>> Sorry for the late response.
>>>
>>>>> -----Original Message-----
>>>>> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
>>>>> Sent: 15 October 2020 17:44
>>>>> To: xen-devel@lists.xenproject.org
>>>>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini <sstabellini@kernel.org>;
>>>>> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
>>>>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
>>>>> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
>>>>> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
>>>>> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
>>>>>
>>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>>
>>>>> This patch introduces a helper the main purpose of which is to check
>>>>> if a domain is using IOREQ server(s).
>>>>>
>>>>> On Arm the current benefit is to avoid calling handle_io_completion()
>>>>> (which implies iterating over all possible IOREQ servers anyway)
>>>>> on every return in leave_hypervisor_to_guest() if there is no active
>>>>> servers for the particular domain.
>>>>> Also this helper will be used by one of the subsequent patches on Arm.
>>>>>
>>>>> This involves adding an extra per-domain variable to store the count
>>>>> of servers in use.
>>>>>
>>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>>> CC: Julien Grall <julien.grall@arm.com>
>>>>>
>>>>> ---
>>>>> Please note, this is a split/cleanup/hardening of Julien's PoC:
>>>>> "Add support for Guest IO forwarding to a device emulator"
>>>>>
>>>>> Changes RFC -> V1:
>>>>> - new patch
>>>>>
>>>>> Changes V1 -> V2:
>>>>> - update patch description
>>>>> - guard helper with CONFIG_IOREQ_SERVER
>>>>> - remove "hvm" prefix
>>>>> - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
>>>>> - put suitable ASSERT()s
>>>>> - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
>>>>> - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
>>>>> ---
>>>>> xen/arch/arm/traps.c | 15 +++++++++------
>>>>> xen/common/ioreq.c | 7 ++++++-
>>>>> xen/include/xen/ioreq.h | 14 ++++++++++++++
>>>>> xen/include/xen/sched.h | 1 +
>>>>> 4 files changed, 30 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
>>>>> index 507c095..a8f5fdf 100644
>>>>> --- a/xen/arch/arm/traps.c
>>>>> +++ b/xen/arch/arm/traps.c
>>>>> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
>>>>> struct vcpu *v = current;
>>>>>
>>>>> #ifdef CONFIG_IOREQ_SERVER
>>>>> - bool handled;
>>>>> + if ( domain_has_ioreq_server(v->domain) )
>>>>> + {
>>>>> + bool handled;
>>>>>
>>>>> - local_irq_enable();
>>>>> - handled = handle_io_completion(v);
>>>>> - local_irq_disable();
>>>>> + local_irq_enable();
>>>>> + handled = handle_io_completion(v);
>>>>> + local_irq_disable();
>>>>>
>>>>> - if ( !handled )
>>>>> - return true;
>>>>> + if ( !handled )
>>>>> + return true;
>>>>> + }
>>>>> #endif
>>>>>
>>>>> if ( likely(!v->arch.need_flush_to_ram) )
>>>>> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
>>>>> index bcd4961..a72bc0e 100644
>>>>> --- a/xen/common/ioreq.c
>>>>> +++ b/xen/common/ioreq.c
>>>>> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
>>>>> struct ioreq_server *s)
>>>>> {
>>>>> ASSERT(id < MAX_NR_IOREQ_SERVERS);
>>>>> - ASSERT(!s || !d->ioreq_server.server[id]);
>>>>> + ASSERT(d->ioreq_server.server[id] ? !s : !!s);
>>>> That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?
>>> ok, looks like it will work.
>>>
>>>
>>>> Paul
>>>>
>>>>> d->ioreq_server.server[id] = s;
>>>>> +
>>>>> + if ( s )
>>>>> + d->ioreq_server.nr_servers++;
>>>>> + else
>>>>> + d->ioreq_server.nr_servers--;
>>>>> }
>>>>>
>>>>> #define GET_IOREQ_SERVER(d, id) \
>>>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
>>>>> index 7b03ab5..0679fef 100644
>>>>> --- a/xen/include/xen/ioreq.h
>>>>> +++ b/xen/include/xen/ioreq.h
>>>>> @@ -55,6 +55,20 @@ struct ioreq_server {
>>>>> uint8_t bufioreq_handling;
>>>>> };
>>>>>
>>>>> +#ifdef CONFIG_IOREQ_SERVER
>>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>>>> +{
>>>>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
>>>>> +
>>>> This seems like an odd place to put such an assertion.
>>> I might miss something or interpreted incorrectly but these asserts are
>>> the result of how I understood the review comment on previous version [1].
>>>
>>> I will copy a comment here for the convenience:
>>> "This is safe only when d == current->domain and it's not paused,
>>> or when they're distinct and d is paused. Otherwise the result is
>>> stale before the caller can inspect it. This wants documenting by
>>> at least a comment, but perhaps better by suitable ASSERT()s."
>> The way his reply was worded, I think Paul was wondering about the
>> place where you put the assertion, not what you actually assert.
>
> Shall I put the assertion at the call sites of this helper instead?

Since Paul raised the question, I expect this is a question to him
rather than me?

Jan
RE: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: 11 November 2020 13:28
> To: Oleksandr <olekstysh@gmail.com>
> Cc: 'Oleksandr Tyshchenko' <oleksandr_tyshchenko@epam.com>; 'Stefano Stabellini'
> <sstabellini@kernel.org>; 'Julien Grall' <julien@xen.org>; 'Volodymyr Babchuk'
> <Volodymyr_Babchuk@epam.com>; 'Andrew Cooper' <andrew.cooper3@citrix.com>; 'George Dunlap'
> <george.dunlap@citrix.com>; 'Ian Jackson' <iwj@xenproject.org>; 'Wei Liu' <wl@xen.org>; 'Julien Grall'
> <julien.grall@arm.com>; paul@xen.org; xen-devel@lists.xenproject.org
> Subject: Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
>
> On 11.11.2020 09:41, Oleksandr wrote:
> >
> > On 11.11.20 10:08, Jan Beulich wrote:
> >
> > Hi Jan
> >
> >> On 10.11.2020 21:53, Oleksandr wrote:
> >>> On 20.10.20 13:51, Paul Durrant wrote:
> >>>
> >>> Hi Paul.
> >>>
> >>> Sorry for the late response.
> >>>
> >>>>> -----Original Message-----
> >>>>> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
> >>>>> Sent: 15 October 2020 17:44
> >>>>> To: xen-devel@lists.xenproject.org
> >>>>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini
> <sstabellini@kernel.org>;
> >>>>> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> >>>>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
> >>>>> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
> >>>>> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
> >>>>> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
> >>>>>
> >>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> >>>>>
> >>>>> This patch introduces a helper the main purpose of which is to check
> >>>>> if a domain is using IOREQ server(s).
> >>>>>
> >>>>> On Arm the current benefit is to avoid calling handle_io_completion()
> >>>>> (which implies iterating over all possible IOREQ servers anyway)
> >>>>> on every return in leave_hypervisor_to_guest() if there is no active
> >>>>> servers for the particular domain.
> >>>>> Also this helper will be used by one of the subsequent patches on Arm.
> >>>>>
> >>>>> This involves adding an extra per-domain variable to store the count
> >>>>> of servers in use.
> >>>>>
> >>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> >>>>> CC: Julien Grall <julien.grall@arm.com>
> >>>>>
> >>>>> ---
> >>>>> Please note, this is a split/cleanup/hardening of Julien's PoC:
> >>>>> "Add support for Guest IO forwarding to a device emulator"
> >>>>>
> >>>>> Changes RFC -> V1:
> >>>>> - new patch
> >>>>>
> >>>>> Changes V1 -> V2:
> >>>>> - update patch description
> >>>>> - guard helper with CONFIG_IOREQ_SERVER
> >>>>> - remove "hvm" prefix
> >>>>> - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
> >>>>> - put suitable ASSERT()s
> >>>>> - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
> >>>>> - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
> >>>>> ---
> >>>>> xen/arch/arm/traps.c | 15 +++++++++------
> >>>>> xen/common/ioreq.c | 7 ++++++-
> >>>>> xen/include/xen/ioreq.h | 14 ++++++++++++++
> >>>>> xen/include/xen/sched.h | 1 +
> >>>>> 4 files changed, 30 insertions(+), 7 deletions(-)
> >>>>>
> >>>>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> >>>>> index 507c095..a8f5fdf 100644
> >>>>> --- a/xen/arch/arm/traps.c
> >>>>> +++ b/xen/arch/arm/traps.c
> >>>>> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
> >>>>> struct vcpu *v = current;
> >>>>>
> >>>>> #ifdef CONFIG_IOREQ_SERVER
> >>>>> - bool handled;
> >>>>> + if ( domain_has_ioreq_server(v->domain) )
> >>>>> + {
> >>>>> + bool handled;
> >>>>>
> >>>>> - local_irq_enable();
> >>>>> - handled = handle_io_completion(v);
> >>>>> - local_irq_disable();
> >>>>> + local_irq_enable();
> >>>>> + handled = handle_io_completion(v);
> >>>>> + local_irq_disable();
> >>>>>
> >>>>> - if ( !handled )
> >>>>> - return true;
> >>>>> + if ( !handled )
> >>>>> + return true;
> >>>>> + }
> >>>>> #endif
> >>>>>
> >>>>> if ( likely(!v->arch.need_flush_to_ram) )
> >>>>> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
> >>>>> index bcd4961..a72bc0e 100644
> >>>>> --- a/xen/common/ioreq.c
> >>>>> +++ b/xen/common/ioreq.c
> >>>>> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
> >>>>> struct ioreq_server *s)
> >>>>> {
> >>>>> ASSERT(id < MAX_NR_IOREQ_SERVERS);
> >>>>> - ASSERT(!s || !d->ioreq_server.server[id]);
> >>>>> + ASSERT(d->ioreq_server.server[id] ? !s : !!s);
> >>>> That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?
> >>> ok, looks like it will work.
> >>>
> >>>
> >>>> Paul
> >>>>
> >>>>> d->ioreq_server.server[id] = s;
> >>>>> +
> >>>>> + if ( s )
> >>>>> + d->ioreq_server.nr_servers++;
> >>>>> + else
> >>>>> + d->ioreq_server.nr_servers--;
> >>>>> }
> >>>>>
> >>>>> #define GET_IOREQ_SERVER(d, id) \
> >>>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
> >>>>> index 7b03ab5..0679fef 100644
> >>>>> --- a/xen/include/xen/ioreq.h
> >>>>> +++ b/xen/include/xen/ioreq.h
> >>>>> @@ -55,6 +55,20 @@ struct ioreq_server {
> >>>>> uint8_t bufioreq_handling;
> >>>>> };
> >>>>>
> >>>>> +#ifdef CONFIG_IOREQ_SERVER
> >>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
> >>>>> +{
> >>>>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
> >>>>> +
> >>>> This seems like an odd place to put such an assertion.
> >>> I might miss something or interpreted incorrectly but these asserts are
> >>> the result of how I understood the review comment on previous version [1].
> >>>
> >>> I will copy a comment here for the convenience:
> >>> "This is safe only when d == current->domain and it's not paused,
> >>> or when they're distinct and d is paused. Otherwise the result is
> >>> stale before the caller can inspect it. This wants documenting by
> >>> at least a comment, but perhaps better by suitable ASSERT()s."
> >> The way his reply was worded, I think Paul was wondering about the
> >> place where you put the assertion, not what you actually assert.
> >
> > Shall I put the assertion at the call sites of this helper instead?
>
> Since Paul raised the question, I expect this is a question to him
> rather than me?

If it is indeed a question for me then yes, put the assertion where it is clear why it is needed. domain_has_ioreq_server() is essentially a trivial accessor function; it's not the appropriate place.

Paul

>
> Jan
Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
On 11.11.20 15:27, Jan Beulich wrote:

Hi Jan.

>
>>>>>> }
>>>>>>
>>>>>> #define GET_IOREQ_SERVER(d, id) \
>>>>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
>>>>>> index 7b03ab5..0679fef 100644
>>>>>> --- a/xen/include/xen/ioreq.h
>>>>>> +++ b/xen/include/xen/ioreq.h
>>>>>> @@ -55,6 +55,20 @@ struct ioreq_server {
>>>>>> uint8_t bufioreq_handling;
>>>>>> };
>>>>>>
>>>>>> +#ifdef CONFIG_IOREQ_SERVER
>>>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>>>>> +{
>>>>>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
>>>>>> +
>>>>> This seems like an odd place to put such an assertion.
>>>> I might miss something or interpreted incorrectly but these asserts are
>>>> the result of how I understood the review comment on previous version [1].
>>>>
>>>> I will copy a comment here for the convenience:
>>>> "This is safe only when d == current->domain and it's not paused,
>>>> or when they're distinct and d is paused. Otherwise the result is
>>>> stale before the caller can inspect it. This wants documenting by
>>>> at least a comment, but perhaps better by suitable ASSERT()s."
>>> The way his reply was worded, I think Paul was wondering about the
>>> place where you put the assertion, not what you actually assert.
>> Shall I put the assertion at the call sites of this helper instead?
> Since Paul raised the question, I expect this is a question to him
> rather than me?
Yes, it was primarily a question to Paul, but I wanted to hear your
opinion as well. Sorry for the confusion.

--
Regards,

Oleksandr Tyshchenko
Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() [ In reply to ]
On 11.11.20 18:28, Paul Durrant wrote:

Hi Paul.

>>
>>>>>>> d->ioreq_server.server[id] = s;
>>>>>>> +
>>>>>>> + if ( s )
>>>>>>> + d->ioreq_server.nr_servers++;
>>>>>>> + else
>>>>>>> + d->ioreq_server.nr_servers--;
>>>>>>> }
>>>>>>>
>>>>>>> #define GET_IOREQ_SERVER(d, id) \
>>>>>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
>>>>>>> index 7b03ab5..0679fef 100644
>>>>>>> --- a/xen/include/xen/ioreq.h
>>>>>>> +++ b/xen/include/xen/ioreq.h
>>>>>>> @@ -55,6 +55,20 @@ struct ioreq_server {
>>>>>>> uint8_t bufioreq_handling;
>>>>>>> };
>>>>>>>
>>>>>>> +#ifdef CONFIG_IOREQ_SERVER
>>>>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
>>>>>>> +{
>>>>>>> + ASSERT((current->domain == d) || atomic_read(&d->pause_count));
>>>>>>> +
>>>>>> This seems like an odd place to put such an assertion.
>>>>> I might miss something or interpreted incorrectly but these asserts are
>>>>> the result of how I understood the review comment on previous version [1].
>>>>>
>>>>> I will copy a comment here for the convenience:
>>>>> "This is safe only when d == current->domain and it's not paused,
>>>>> or when they're distinct and d is paused. Otherwise the result is
>>>>> stale before the caller can inspect it. This wants documenting by
>>>>> at least a comment, but perhaps better by suitable ASSERT()s."
>>>> The way his reply was worded, I think Paul was wondering about the
>>>> place where you put the assertion, not what you actually assert.
>>> Shall I put the assertion at the call sites of this helper instead?
>> Since Paul raised the question, I expect this is a question to him
>> rather than me?
> If it is indeed a question for me then yes, put the assertion where it is clear why it is needed. domain_has_ioreq_server() is essentially a trivial accessor function; it's not the appropriate place.

Got it. Thank you for the clarification.

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Regards,

Oleksandr Tyshchenko